Add required limits.h header.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@16789 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavutil/internal.h

@@ -30,6 +30,7 @@
 #    define NDEBUG
 #endif
 
+#include <limits.h>
 #include <stdint.h>
 #include <stddef.h>
 #include <assert.h>